• Continue partners.

Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Four types of repetition.
• Lab.

Preliminaries

Admin

• I am supposed to remind you that Friday is the Withdraw deadline.
• There are still flu vaccines left at SHACS.
• Exam 2 returned.
  • While you may certainly discuss answers with your colleagues, please do not share your grade with colleagues.
• Exam 2 answer key forthcoming soon. (Still some delays due to a variety of issues.)
• Review sessions this week:
  • Wednesday, 8pm (Caleb)
  • Thursday, 10am (SamR)
  • Thursday, 8pm (Erin)

Upcoming Work

• Reading for Wednesday: Randomness.
• HW 6 due TONIGHT!
• Exam 3 distributed in draft form.
  • No corrections until after class on Wednesday.
  • The code file is not yet ready.
• NO LAB WRITEUP.

Extra Credit Opportunities

• If possible, send me these in advance.

Academic

• Any visit to the current show in the Faulconer gallery.
• Learning Deconstructed Workshop Series, Tuesdays at 11 in JRC 209.
• Any activity with Visiting Musician and Sound Artist Ellen Fullman. (Yes, that includes Drinks @ Lonnski's on Thursday.)
• CS Table Tuesday: Why people support and bully online.
• CS Extras Thursday: Bluetooth, Robots, and CS 161.
• Sexual Misconduct at Grinnell College: Results from the 2013 and 2015 Sexual Conduct Surveys. 1-3 pm, November 8, JRC 101.

Peer Support

Regular Peer Support

• Pals of PALS, pals@grinnell.edu, normally Saturday at 7:45 am (breakfast included), Sunday at 4:45, and Mondays at 4:45. Requires sign up in advance.
• Socrates Cafe', Saturdays, Younker, 2pm.
• Pun Club, Saturdays, 4pm, Way over Younker.

Upcoming Peer Support

• November 14, Orchestra Concert, Sebring Lewis, 7:30 p.m.
• Women's Basketball Opening Game, 1pm, Nov. 15, vs. Silver Lake.
• One-act Festival Dec. 5 & 6.

Other Good Stuff to Do

• VOTE today

Questions

Do you have any observations after helping people with Part C?

Remember that when you decide to split the region, you have to recurse twice - either for the left half and right half, or for the top half and bottom half.

Remember that left, top, width, and height all have to be integers. In some cases, you won't be able to divide exactly.

What angle did you use for the swirly one?

I think I used (/ pi 32)..

The original "painting" was made by selecting left:100, top: 50, width: 200, height:260.

When replacing, I used left: 110, top: 60, width: 180, height: 240, which I think preserved the aspect ratio of the image.

Contrasting map, for-each, repeat, and recursion

map:

• Input: function and one or more lists
• Output: list
• Operation: It applies the function to each element of the list. The ith element of the output list is the result of applying the function to the ith element of the input list.
• Complexity (multiple lists): (map + (list 1 2 3) (list 4 5 6)) For multiple lists, it takes the ith element of each input list and then applies the function.
• Complexity: If the lists are different lengths, it tells you that you need the lists to have the same length lists.
• Complexity: The procedure needs to expect the appropriate number of parameters.

for-each:

• Input: function/procedure and one or more lists
• Output: We don't care; called for side effects
• Operation: It applies the function to each element of the list, ignoring the result. (In contrast to map, which shoves the results together into a list).

repeat:

• Input: an integer (n), a procedure of zero or more parameters (proc), potential parameters to that procedure (val1, val2, val3, ...)
• Note: The procedure can have no parameters.
• Output: Irrelevant; called for the effect of calling procedure.
• Operation: Repeats exactly the same step again and again and again (n times) Only useful if we have operations with side-effects.

recursion:

• Problem: No such function; It's more of a technique
• Input: Almost anything
• Output: Almost anything
• Operation: Repeatedly do something

If you go from a list to a list of the same length: map

If you do things mostly for side effects: for-each or repeat

General case: recursion

• Lists to numbers
• Numbers to lists
• Lists to different length lists
• Numbers to numbers
• ...

Lab